Process for the production of ethylene oxide

ABSTRACT

The invention relates to a process for the production of ethylene oxide, comprising the steps of: producing ethylene by converting a stream comprising an oxygenate into a stream comprising ethylene and ethane; producing ethylene oxide by subjecting ethylene and ethane from the stream comprising ethylene and ethane to oxidation conditions resulting in a stream comprising ethylene oxide, unconverted ethylene and ethane; and recovering ethylene oxide from the stream comprising ethylene oxide, unconverted ethylene and ethane.

The present application is a continuation of U.S. application Ser. No.13/980,927 filed Sep. 30, 2013, which is the National Stage (§371) ofInternational Application PCT/EP2012/050988, filed Jan. 23, 2012, andwhich claims the benefit of European Patent Application No. 11151793.4filed Jan. 24, 2011, all of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a process for the production ofethylene oxide.

In recent years, increasing attention has been given to the explorationand utilisation of natural gas resources around the globe. Adisadvantage of natural gas with respect to oil is the difficulty totransport large volumes of natural gas from the source to the market.One way of efficiently transporting natural gas is by liquefying thenatural gas and to transport the liquefied natural gas (LNG).

Another way is to convert the methane in the natural gas to liquidderivatives, which can also be transported at relative ease. One liquidderivative of interest may for instance be monoethylene glycol (MEG).MEG is a liquid at room temperature and can therefore be suitablytransported. MEG is produced by reacting ethylene oxide with water.

In WO200236532, a process for preparing ethylene oxide from methane isdescribed. In the process of WO200236532, methane is converted tomethanol, via syngas, and the methanol is subsequently converted to aproduct stream comprising ethylene via a Methanol-to-Olefins (MTO)process. The product steam comprises, in addition to ethylene, alsoparaffinic compounds, such as ethane. The production of ethane as aby-product in said ethylene production process is for example alsodisclosed in U.S. Pat. No. 5,990,369 and U.S. Pat. No. 7,132,580.

These paraffinic compounds are separated from the ethylene prior tosending the ethylene to the ethylene oxidation unit. The ethane istypically sent as fuel to a furnace. However, the separation of ethanefrom ethylene leads to loss of ethylene as part of the ethylene will beremoved together with the ethane, in particular if a high purity of theethylene is sought. Consequently, ethylene oxide and thus MEG yields ofthe process, based on the methane provided, are reduced.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a process for theproduction of ethylene oxide by producing ethylene by conversion of anoxygenate, such as methanol, and producing ethylene oxide by oxidationof said ethylene, which process does not have the above drawback.

Surprisingly, it was found that the above drawback is avoided by meansof an integrated process wherein ethylene is produced by converting astream comprising an oxygenate into a stream comprising ethylene andethane, wherein ethylene and ethane from the latter stream are subjectedto oxidation conditions resulting in the desired ethylene oxide.

Accordingly, the present invention relates to a process for theproduction of monoethylene glycol, comprising the steps of:

producing ethylene by converting a stream comprising an oxygenate into afirst product stream comprising ethylene and ethane through anoxygenate-to-olefins process;

producing ethylene oxide by subjecting ethylene and ethane from thefirst product stream comprising ethylene and ethane to oxidationconditions resulting in a second product stream comprising ethyleneoxide, unconverted ethylene and ethane;

recovering ethylene oxide from the second product stream comprisingethylene oxide, unconverted ethylene and ethane; and

converting the ethylene oxide to monoethylene glycol through anhydrolysis reaction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a preferred embodiment of theinvention.

FIG. 2 is a schematic illustration of a second preferred embodiment ofthe invention.

DETAILED DESCRIPTION

An advantage of the present invention is that no ethane has to beseparated from the ethylene containing product stream that results fromthe ethylene production step. This results in a much simpler overallprocess using less separation processes and equipment, as compared tofor example the process of FIG. 1 of above-mentioned U.S. Pat. No.5,990,369 as explained at column 10, line 26 and further of said U.S.Pat. No. 5,990,369 and said WO200236532.

In addition, the non-separated ethane advantageously functions as aballast gas in the next ethylene oxidation step so that no orsubstantially less additional ballast gas needs to be added. Because anoxidizing agent is required, it is important to control the safeoperability of the reaction mixture, which can generally be done byadding a ballast gas. Common ballast gases in the production of ethyleneoxide by oxidation of ethylene, are nitrogen and methane.

Still further, separation of the stream comprising ethylene and ethaneresulting from the ethylene production step of the present process isadvantageously automatically, and at least partially, effected in theethylene oxide production step wherein the ethylene is consumed andconverted into ethylene oxide which can be separated more easily fromthe non-consumed ethane.

All these and other advantages result in a substantial reduction ofexpenditure, for example savings on costs for compression,refrigeration, etc. needed for separating ethane from the ethylene.These and other advantages are further described below.

GB1314613 discloses the use of ethane as a ballast gas in the productionof ethylene oxide from ethylene. However, the integrated process of thepresent invention is not disclosed and is neither suggested inGB1314613.

The ethylene oxidation step in the present process results in a streamcomprising ethylene oxide, unconverted ethylene and ethane. The ethyleneoxide can be recovered easily from such stream by means of methods knownto the skilled person. That is to say, ethylene oxide may be separatedfrom said stream comprising ethylene oxide, unconverted ethylene andethane resulting in a stream comprising unconverted ethylene and ethane.The unconverted ethylene and the ethane from the latter stream may berecycled within the present process and advantageously be converted andre-used, respectively, after such recycle. After ethylene oxide isseparated from said stream comprising ethylene oxide, unconvertedethylene and ethane and before such recycle of the remaining unconvertedethylene and ethane, any carbon dioxide is removed. That is to say,either part or all carbon dioxide is removed. Said carbon dioxide may beproduced in the ethylene oxide production step. Ways of removing carbondioxide, such as a caustic wash, are known to the skilled person. Theremoved carbon dioxide may be used to produce methanol, from hydrogenand said carbon dioxide and optionally carbon monoxide, which methanolcan then be used as a feedstock for the ethylene production stepcomprising oxygenate conversion of the present invention.

Unconverted ethylene, and optionally ethane, from the stream comprisingethylene oxide, unconverted ethylene and ethane resulting from the stepof producing ethylene oxide may be recycled to that step of producingethylene oxide. That is to say, either part or all unconverted ethylene,and optionally ethane, is recycled in such way. The recycled unconvertedethylene is then advantageously converted as yet in that ethyleneoxidation step. Further, the recycled ethane is then advantageouslyre-used as a ballast gas in that ethylene oxidation step. In thisembodiment, preferably, a stream comprising unconverted ethylene andethane is separated from the stream comprising ethylene oxide,unconverted ethylene and ethane resulting from the step of producingethylene oxide, and is then recycled to the step of producing ethyleneoxide. Such recycle has both said advantages in that conversion ofunconverted ethylene into ethylene oxide is effected as yet, whereasre-use of ethane as a ballast gas is also effected at the same time.

Where in the present specification reference is made to recycling to the“step of producing ethylene oxide”, “ethylene oxide production step” or“ethylene oxidation step”, such step not only covers the step(s) ofproduction of the desired product in question but also the step(s) ofwork-up of the product stream in question.

An embodiment of the present invention is shown in FIG. 1.

In the flow scheme of FIG. 1, stream 1 comprising a feed containing anoxygenate is fed to ethylene production unit 2. Stream 3 comprisingethylene and ethane and stream 4 comprising an oxidizing agent, such ashigh-purity oxygen or air, are fed to ethylene oxide production unit 5.Stream 6 comprising ethylene oxide, unconverted ethylene, ethane andcarbon dioxide is sent to ethylene oxide separation unit 7. Ethyleneoxide is recovered via stream 8. Further, stream 9 comprisingunconverted ethylene, ethane and carbon dioxide is split into twosubstreams 9 a and 9 b. Substream 9 a is recycled to ethylene oxideproduction unit 5. Substream 9 b is fed to carbon dioxide removal unit10. Stream 11 comprising unconverted ethylene and ethane is split intotwo substreams 11 a and 11 b. Substream 11 a is recycled to ethyleneoxide production unit 5. Substream 11 b is fed to ethylene/ethaneseparation unit 12. Stream 13 comprising unconverted ethylene isrecycled to ethylene oxide production unit 5. Stream 14 comprisingethane may be discarded. Further, a third stream may be separated inethylene/ethane separation unit 12, namely a top bleed stream comprisinguncondensable components, such as oxygen and/or argon (said third streamnot shown in FIG. 1). Still further, stream 3 may be subjected tohydrotreatment in a hydrotreater unit before entering ethylene oxideproduction unit 5 (said hydrotreater unit not shown in FIG. 1) toconvert any acetylene present. In general, in the conversion of anoxygenate, such as methanol, into ethylene hydrogen may be produced as aby-product. Separating hydrogen from the stream comprising ethylene andethane is not essential in terms of obtaining the advantages of thepresent invention as described herein. It is even preferred thathydrogen, if any, is not separated from the latter stream. In this way,at least part of the hydrogen may be used to convert at least part ofthe acetylene.

In the ethylene oxide production step of the present process, ethyleneoxide is produced by subjecting ethylene and ethane from the streamcomprising ethylene and ethane, originating from the ethylene productionstep, to oxidation conditions resulting in a stream comprising ethyleneoxide, unconverted ethylene and ethane.

An advantage of the present process is that the product stream resultingfrom the ethylene production step also comprises ethane, in addition toethylene that is to be oxidized in the next step. Ethane is a suitableballast gas in the oxidation of ethylene. As discussed above, normallynitrogen or methane is added as a ballast gas in the oxidation ofethylene. Now that in the present invention, ethane present in theethylene containing product stream resulting from the ethyleneproduction step functions as a ballast gas in the ethylene oxideproduction step, no or substantially less of a separate ballast gas,such as nitrogen or methane, has to be added. This results in a muchsimpler and more efficient ethylene oxidation process.

In the ethylene oxide production step of the present process, ethyleneand ethane from the stream comprising ethylene and ethane are contactedwith an oxidizing agent. The oxidizing agent may be high-purity oxygenor air, but is preferably high-purity oxygen which may have a puritygreater than 90%, preferably greater than 95%, more preferably greaterthan 99%, and most preferably greater than 99.9%. Typical reactionpressures are 1-40 bar, suitably 10-30 bar, and typical reactiontemperatures are 100-400° C., suitably 200-300° C.

Further, the amounts of ethylene and ethane, respectively, as fed to theethylene oxide production step of the present process, may be of from 10to 90 wt. %, suitably of from 20 to 80 wt. % of ethylene, and 90 to 10wt. %, suitably of from 80 to 20 wt. % of ethane, respectively, all saidamounts based on the total amount of the stream or the streamscomprising ethylene and/or ethane as fed to said ethylene oxideproduction step.

The minimum amount of ethylene as referred to above may be 1 wt. %, 5wt. %, wt. %, 20 wt. %, 25 wt. %, 30 wt. % or 35 wt. %. The maximumamount of ethylene as referred to above may be 99 wt. %, 95 wt. %, 90wt. %, 80 wt. %, 70 wt. %, 60 wt. %, 55 wt. %, 50 wt. % or 45 wt. %. Theminimum amount of ethane as referred to above may be 1 wt. %, 5 wt. %,10 wt. %, 20 wt. %, 25 wt. %, 30 wt. % or 35 wt. %. The maximum amountof ethane as referred to above may be 99 wt. %, 95 wt. %, 90 wt. %, 80wt. %, 70 wt. %, 60 wt. %, 55 wt. %, 50 wt. % or 45 wt. %.

In case the ethylene production step comprising oxygenate conversiondoes not result in sufficient ethane for use as ballast gas in theethylene oxide production step, additional ethane may be added to theethylene oxide production step. The source of the ethane may be anysource. For example, additional ethane may originate from steam crackinga hydrocarbon stream as further discussed below. Additional ethane maybe added in such amount that the amount of ethane as referred to abovefalls within any of the above-mentioned ranges for ethane.

Further, it is preferred that in the ethylene oxide production step ofthe present process, the ethylene and ethane are contacted with acatalyst, preferably a silver containing catalyst. A typical reactor forthe ethylene oxide production step consists of an assembly of tubes thatare packed with catalyst. A coolant may surround the reactor tubes,removing the reaction heat and permitting temperature control.

In case a silver containing catalyst is used in the ethylene oxideproduction step of the present process, the silver in the silvercontaining catalyst is preferably in the form of silver oxide. Preferredis a catalyst comprising particles wherein silver is deposited on acarrier. Suitable carrier materials include refractory materials, suchas alumina, magnesia, zirconia, silica and mixtures thereof. Thecatalyst may also contain a promoter component, e.g. rhenium, tungsten,molybdenum, chromium, nitrate- or nitrite-forming compounds andcombinations thereof. Preferably, the catalyst is a pelletized catalyst,for example in the form of a fixed catalyst bed, or a powdered catalyst,for example in the form of a fluidized catalyst bed.

The nature of the ethylene oxidation catalyst, if any, is not essentialin terms of obtaining the advantages of the present invention asdescribed herein. The amount of the ethylene oxidation catalyst isneither essential. If a catalyst is used, preferably a catalyticallyeffective amount of the catalyst is used, that is to say an amountsufficient to promote the ethylene oxidation reaction. Although aspecific quantity of catalyst is not critical to the invention,preference may be expressed for use of the catalyst in such an amountthat the gas hourly space velocity (GHSV) is of from 100 to 50,000 hr⁻¹,suitably of from 500 to 20,000 hr⁻¹, more suitably of from 1,000 to10,000 hr⁻¹, most suitably of from 2,000 to 4,000 hr⁻¹.

In the present specification, “GHSV” or gas hourly space velocity is theunit volume of gas at normal temperature and pressure (0° C., 1atmosphere, i.e. 101.3 kPa) passing over one unit volume of catalyst perhour.

A moderator, for example a chlorohydrocarbon such as monochloroethane(ethyl chloride), vinyl chloride or dichloroethane, may be supplied forcatalyst performance control in the ethylene oxide production step ofthe present process. Most suitably, ethyl chloride is used.

Moderators that can be suitably used in the ethylene oxide productionstep of the present process are also disclosed in above-mentionedGB1314613, the disclosure of which is herein incorporated by reference.GB1314613 discloses the use of an inhibitor (that is to say, amoderator), selected from ethylene dichloride, vinyl chloride,dichlorobenzene, monochlorobenzene, dichloromethane, and chlorinatedphenyls, chlorinated biphenyls and chlorinated polyphenyls, in theproduction of ethylene oxide from ethylene.

The nature of the moderator, if any, is not essential in terms ofobtaining the advantages of the present invention as described herein.The amount of the moderator is neither essential. The amount of suchmoderator in the reaction mixture may range from 1 part per million byvolume (ppmv) to 2 vol. %, suitably 1 to 1,000 ppmv. The minimum amountof moderator in the reaction mixture may be 0.1 ppmv, 0.2 ppmv, 0.5ppmv, 1 ppmv, 2 ppmv, 5 ppmv, 10 ppmv or 50 ppmv. The maximum amount ofmoderator in the reaction mixture may be 2 vol. %, 1 vol. %, 1,000 ppmv,800 ppmv or 700 ppmv.

A suitable range for the amount of moderator that can be used in theethylene oxide production step of the present process is also disclosedin above-mentioned GB1314613 in relation to the above-mentioned group ofspecific inhibitors (that is to say, moderators) as disclosed in saidGB1314613, the disclosure of which is herein incorporated by reference.

Examples of ethylene oxidation processes, including catalysts and otherprocess conditions, are for example disclosed in US20090281345 andabove-mentioned GB1314613, the disclosures of which are hereinincorporated by reference. All of these ethylene oxidation processes aresuitable for the ethylene oxidation step of the present invention.

The process of the present invention comprises a step of producingethylene which step comprises converting a stream comprising anoxygenate. In this step, the oxygenate in the stream comprising theoxygenate is converted to an olefin (said ethylene) by anOxygenate-to-Olefins (OTO) process.

Within the present specification, an “oxygenate” means a compound whichcontains at least one oxygen-bonded alkyl group. The alkyl grouppreferably is a C1-C4 alkyl group, more preferably a C1-C2 alkyl groupand most preferably a C1 alkyl group. The oxygenate may comprise one ormore of such oxygen-bonded C1-C4 alkyl groups. Preferably, the oxygenatecomprises one or two oxygen-bonded C1-C4 alkyl groups. More preferablyan oxygenate is used having at least one C1 or C2 alkyl group, stillmore preferably at least one C1 alkyl group.

Preferably the oxygenate is chosen from the group of alcohols anddialkyl ethers consisting of dimethylether, diethylether,methylethylether, methanol, ethanol and isopropanol, and mixturesthereof. Most preferably the oxygenate is methanol or dimethylether, ora mixture thereof.

In the process of the present invention, a stream comprising anoxygenate is converted into a stream comprising ethylene and ethane. Theethane from the stream resulting from said step of the present processis produced as a by-product by conversion of the desired ethyleneproduct.

Examples of oxygenate-to-olefins processes, including catalysts andother process conditions, are for example disclosed in US20060020155 (inparticular in paragraphs [0116] to [0135] thereof), US20070203380,US20070155999, US20090187058, US20100298619, US20100268007, U.S. Pat.No. 8,269,056, U.S. Pat. No. 8,884,090 and US20100268009, thedisclosures of which are herein incorporated by reference. All of theseoxygenate-to-olefins processes are suitable for the ethylene productionstep of the present invention said step comprising oxygenate conversion.

In said ethylene production step of the present invention, the streamcomprising an oxygenate is contacted with a catalyst.

Catalysts suitable for converting the oxygenate comprise molecularsieve. Such molecular sieve-comprising catalysts typically also includebinder materials, matrix material and optionally fillers. Suitablematrix materials include clays, such as kaolin. Suitable bindermaterials include silica, alumina, silica-alumina, titania and zirconia,wherein silica is preferred due to its low acidity.

For example, catalysts as described in above-mentioned US20060020155 aresuitable for converting said oxygenate comprising stream. Preferably,such catalyst is a molecular sieve catalyst.

Suitable molecular sieves are silicoaluminophosphates (SAPO), such asSAPO-17, -18, 34, -35, -44, but also SAPO-5, -8, -11, -20, -31, -36, 37,-40, -41, -42, -47 and -56; aluminophosphates (AlPO) and metalsubstituted (silico)aluminophosphates (MeAlPO), wherein the Me in MeAlPOrefers to a substituted metal atom, including metal selected from one ofGroup IA, IIA, IB, IIIB, IVB, VB, VIB, VIIB, VIIIB and Lanthanides ofthe Periodic Table of Elements. Preferably Me is selected from one ofthe group consisting of Co, Cr, Cu, Fe, Ga, Ge, Mg, Mn, Ni, Sn, Ti, Znand Zr.

Alternatively, the conversion of the oxygenate may be accomplished bythe use of an aluminosilicate-comprising catalyst, in particular azeolite-comprising catalyst. Suitable catalysts include those containinga zeolite of the ZSM group, in particular of the MFI type, such asZSM-5, the MTT type, such as ZSM-23, the TON type, such as ZSM-22, theMEL type, such as ZSM-11, and the FER type. Other suitable zeolites arefor example zeolites of the STF-type, such as SSZ-35, the SFF type, suchas SSZ-44 and the EU-2 type, such as ZSM-48.

Aluminosilicate-comprising catalyst, and in particularzeolite-comprising catalyst are preferred when an olefinic co-feed isfed to the oxygenate conversion zone together with oxygenate, forincreased production of ethylene and propylene.

Preferred catalysts comprise a more-dimensional zeolite, in particularof the MEI type, more in particular ZSM-5, or of the MEL type, such aszeolite ZSM-11. Such zeolites are particularly suitable for convertingolefins, including iso-olefins, to ethylene and/or propylene. Thezeolite having more-dimensional channels has intersecting channels in atleast two directions. So, for example, the channel structure is formedof substantially parallel channels in a first direction, andsubstantially parallel channels in a second direction, wherein channelsin the first and second directions intersect. Intersections with afurther channel type are also possible. Preferably, the channels in atleast one of the directions are 10-membered ring channels. A preferredMFI-type zeolite has a silica-to-alumina ratio, SAR, of at least 60,preferably at least 80. More preferred MR-type zeolite has asilica-to-alumina ratio, SAR, in the range of 60 to 150, preferably inthe range of 80 to 100.

In one embodiment the catalysts include catalysts comprising one or morezeolites having one-dimensional 10-membered ring channels, i.e.one-dimensional 10-membered ring channels, which are not intersected byother channels. Preferred examples are zeolites of the MTT and/or TONtype. In a particularly example of this embodiment the catalystcomprises in addition to one or more more-dimensional zeolite, inparticular of the MFI type, more in particular ZSM-5, or of the MELtype, such as zeolite ZSM-11, an one-dimensional zeolites having10-membered ring channels, such as of the MTT and/or TON type.

The catalyst may further comprise phosphorus as such or in a compound,i.e. phosphorus other than any phosphorus included in the framework ofthe molecular sieve. It is preferred that a MEL or MFI-type zeolitecomprising catalyst additionally comprises phosphorus. The phosphorusmay be introduced by pre-treating the MEL or MR-type zeolites prior toformulating the catalyst and/or by post-treating the formulated catalystcomprising the MEL or MFI-type zeolites. Preferably, the catalystcomprising MEL or MFI-type zeolites comprises phosphorus as such, i.e.in elemental form, or in a compound in an elemental amount of from 0.05to 10 wt. % based on the weight of the formulated catalyst. Aparticularly preferred catalyst comprises phosphorus and MEL or MFI-typezeolite having SAR of in the range of from 60 to 150, more preferably offrom 80 to 100. An even more particularly preferred catalyst comprisesphosphorus and ZSM-5 having SAR of in the range of from 60 to 150, morepreferably of from 80 to 100.

Preferably, the catalyst is a pelletized catalyst, for example in theform of a fixed catalyst bed, or a powdered catalyst, for example in theform of a fluidized catalyst bed.

The nature of the oxygenate-to-olefins catalyst is not essential interms of obtaining the advantages of the present invention as describedherein.

The amount of the oxygenate-to-olefins catalyst is neither essential.Preferably a catalytically effective amount of the catalyst is used,that is to say an amount sufficient to promote the oxygenate-to-olefinsconversion. Although a specific quantity of catalyst is not critical tothe invention, preference may be expressed for use of the catalyst insuch an amount that the gas hourly space velocity (GHSV) is of from 50to 50,000 hr⁻¹, more preferably of from 100 to 20,000 hr⁻¹, mostpreferably of from 150 to 5,000 hr⁻¹.

In said oxygenate-to-olefins process that is part of the process of thepresent invention, typical reaction pressures are 1 mbar to 50 bar,suitably 1-15 bar, and typical reaction temperatures are 200-1000° C.,suitably 250-750° C.

Preferably, the stream comprising an oxygenate additionally comprises atleast a C4 and/or a C5 olefin or, alternatively, a stream comprising atleast a C4 and/or a C5 olefin is co-fed to the step of producingethylene together with the stream comprising an oxygenate.

In general, the product stream resulting from the ethylene productionstep comprising oxygenate conversion in the process of the presentinvention comprises water in addition to ethylene and ethane. Water mayeasily be separated from said product stream, for example by coolingdown the product stream from the reaction temperature to a lowertemperature, for example room temperature, so that the water condensesand can then be separated from the product stream.

After separating water, as described above, the resulting streamcomprising ethylene and ethane, from which the water is separated, maybe further conventionally washed with a caustic solution, in order toneutralize and remove any acid gases present in the latter stream, andthen dried.

In general, in the conversion of an oxygenate, such as methanol, intoethylene, methane may be produced as a by-product. Separating anymethane from the stream comprising ethylene and ethane is not essentialin terms of obtaining the advantages of the present invention asdescribed herein. It is even preferred that methane, if any, is notseparated from the latter stream. In this way, methane may function as aballast gas, in combination with ethane, in the ethylene oxidation step.This is advantageous first of all in that the methane does not have beseparated, which is cumbersome, and secondly in that in a case whereadditional ballast gas needs to be added to the ethylene oxideproduction step, this may no longer be needed as the mixture of methaneand ethane may provide a sufficient amount of ballast gas for theethylene oxide production step.

The process of the present invention comprises a step of producingethylene which comprises converting a stream comprising an oxygenateinto a stream comprising ethylene and ethane as discussed above. Inaddition, the process of the present invention may comprise one or moreother steps of producing ethylene. Such other ethylene productionprocess(es) is (are) to be carried out in a reactor or reactorsdifferent from the reactor wherein a stream comprising an oxygenate isconverted. An example of such other ethylene production process is steamcracking hydrocarbon streams, such as an ethane stream, a naphthastream, a gasoil stream or a hydrowax stream, into ethylene. It isenvisaged that ethylene and ethane originating from converting a streamcomprising an oxygenate into a stream comprising ethylene and ethane asdiscussed above, and ethylene and ethane originating from anotherprocess or other processes of preparing ethylene, such as said steamcracking, may be fed, either in combination or separately, to the stepof oxidation of ethylene into ethylene oxide. Such integrated process isdiscussed below inter alia with reference to steam cracking of an ethanestream.

A preferred embodiment of the present process for the production ofmonoethylene glycol, comprising the steps of:

producing ethylene by converting a stream comprising an oxygenate into afirst product stream comprising ethylene and ethane through anoxygenate-to-olefins process;

producing ethylene oxide by subjecting ethylene and ethane from thefirst product stream comprising ethylene and ethane to oxidationconditions resulting in a second product stream comprising ethyleneoxide, unconverted ethylene and ethane;

recovering ethylene oxide from the second product stream comprisingethylene oxide, unconverted ethylene and ethane; and

converting the ethylene oxide to monoethylene glycol through anhydrolysis reaction.

In the above ethane steam cracking embodiment of the present process,additional ethylene is produced by converting a stream comprising ethaneinto a stream comprising ethylene and unconverted ethane. In the presentinvention, it is also envisaged that additional ethylene is produced byconverting a hydrocarbon stream comprising naphtha, gasoil or hydrowaxinto a stream comprising ethylene and ethane, similar to theabove-mentioned ethane steam cracking embodiment.

That is to say, a preferred embodiment of the present process for theproduction of monoethylene glycol, comprising the steps of:

producing ethylene by converting a stream comprising an oxygenate into afirst product stream comprising ethylene and ethane through anoxygenate-to-olefins process;

producing ethylene oxide by subjecting ethylene and ethane from thefirst product stream comprising ethylene and ethane to oxidationconditions resulting in a second product stream comprising ethyleneoxide, unconverted ethylene and ethane;

recovering ethylene oxide from the second product stream comprisingethylene oxide, unconverted ethylene and ethane; and

converting the ethylene oxide to monoethylene glycol through anhydrolysis reaction.

Preferably, in the above preferred embodiment, said hydrocarbon streamis a stream comprising ethane, naphtha, gasoil or hydrowax or anymixture thereof.

In the present specification, “naphtha” refers to a mixture comprisingsaturated hydrocarbons which have a boiling point ranging from 20 to200° C. Generally, said hydrocarbons have between 5 and 12 carbon atoms.Further, “gasoil” refers to a mixture comprising saturated hydrocarbonswhich have a boiling point ranging from 200 to 600° C., and “hydrowax”refers to a mixture comprising saturated hydrocarbons which have aboiling point ranging from 250 to 700° C.

In the above steam cracking embodiments of the present process, thesteam cracking process is carried out in a reactor different from thereactor used in converting the stream comprising an oxygenate into astream comprising ethylene and ethane.

Further, in the above steam cracking embodiments of the present process,in general hydrogen is produced as a by-product. The hydrogen may beseparated from the product streams using any suitable means known in theart, for example by cryogenic distillation, by pressure swing absorptionwhereby hydrogen absorbs preferentially, or via a hydrogen permeablemembrane. The separated hydrogen may be used to produce methanol, fromsaid hydrogen and carbon monoxide and/or carbon dioxide, which methanolcan then be used as a feedstock for the ethylene production stepcomprising oxygenate conversion of the present invention.

In the above steam cracking embodiments of the present process, theethylene oxidation step also results in a stream comprising ethyleneoxide, unconverted ethylene and ethane. For example, in the ethane steamcracking embodiment of the present process, said “ethane” in the latterstream comprises both ethane by-product that originates from convertinga stream comprising an oxygenate and unconverted ethane that originatesfrom ethane steam cracking.

Also in the above steam cracking embodiments of the present process, asalready discussed above in general, it is preferred that a streamcomprising unconverted ethylene and ethane is separated from the streamcomprising ethylene oxide, unconverted ethylene and ethane, that resultsfrom the ethylene oxidation step, and is recycled to the step ofproducing ethylene oxide.

In the above steam cracking embodiments of the present process, ethanefrom the stream comprising ethylene oxide, unconverted ethylene andethane (unconverted ethane and/or by-product ethane) resulting from thestep of producing ethylene oxide may be recycled to the steam crackingstep of producing ethylene. Either part or all ethane is recycled insuch way. This has the advantage that more ethylene may be produced byrecycling ethane (unconverted ethane and/or by-product ethane) whereasethane that is not converted after such recycle will then automaticallybe re-used as a ballast gas in the ethylene oxidation step. That is tosay, also in those embodiments of the present invention where ahydrocarbon stream is cracked in an additional step, which stream is anethane, naphtha, gasoil or hydrowax stream, such recycled ethane may beconverted into ethylene.

Further, in the above steam cracking embodiments of the present process,ethane from the stream comprising ethylene oxide, unconverted ethyleneand ethane (unconverted ethane and/or by-product ethane) resulting fromthe step of producing ethylene oxide may be recycled to both the step ofproducing ethylene oxide and to the steam cracking step of producingethylene. Both types of recycle of ethane are illustrated in FIG. 2, asfurther discussed below, with reference to the ethane steam crackingembodiment.

Where in the present specification reference is made to recycling to the“step of producing ethylene” or “ethylene production step”, or recyclingto the “step of producing ethylene oxide”, “ethylene oxide productionstep” or “ethylene oxidation step”, such steps not only cover thestep(s) of production of the desired product in question but also thestep(s) of work-up of the product stream in question.

Preferably, in the above steam cracking embodiments of the presentprocess, a stream comprising unconverted ethylene and ethane(unconverted ethane and/or by-product ethane) is separated from thestream comprising ethylene oxide, unconverted ethylene and ethane(unconverted ethane and/or by-product ethane) and is recycled to thestep of producing ethylene oxide. Further, preferably, said separatedstream comprising unconverted ethylene and ethane (unconverted ethaneand/or by-product ethane) is further separated into a stream comprisingunconverted ethylene which is recycled to the step of producing ethyleneoxide and a stream comprising ethane (unconverted ethane and/orby-product ethane) which is recycled to the steam cracking step ofproducing ethylene. This is illustrated in FIG. 2, as further discussedbelow, with reference to the ethane steam cracking embodiment.

In addition, advantageously, the latter separation is not critical sothat a complete separation of ethane from ethylene is not needed. In theabove steam cracking embodiments of the present process, ethane is(ethane steam cracking embodiment) or can be (other steam crackingembodiments) starting material in the ethylene production step inquestion and is at the same time ballast gas in the subsequent ethyleneoxide production step. All that matters is that the separated substreamwhich comprises more ethylene than the other separated substream isrecycled to the step of producing ethylene oxide, whereas the otherseparated substream is recycled to the ethylene production step inquestion.

In the flow scheme of FIG. 2, which illustrates the above ethane steamcracking embodiment of the present process, stream 1 comprising a feedcontaining an oxygenate is fed to ethylene production unit 2. Stream 3comprising ethylene and ethane and stream 4 comprising an oxidizingagent, such as high-purity oxygen or air, are fed to ethylene oxideproduction unit 5. Stream 15 comprising a feed containing ethane is fedto ethylene production (steam cracker) unit 16. Stream 17 comprisingethylene and unconverted ethane is fed, via stream 3, to ethylene oxideproduction unit 5. Stream 6 comprising ethylene oxide, unconvertedethylene, ethane and carbon dioxide is sent to ethylene oxide separationunit 7. Ethylene oxide is recovered via stream 8. Further, stream 9comprising unconverted ethylene, ethane and carbon dioxide is split intotwo substreams 9 a and 9 b. Substream 9 a is recycled to ethylene oxideproduction unit 5. Substream 9 b is fed to carbon dioxide removal unit10. Stream 11 comprising unconverted ethylene and ethane is split intotwo substreams 11 a and 11 b. Substream 11 a is recycled to ethyleneoxide production unit 5. Substream 11 b is fed to ethylene/ethaneseparation unit 12. Stream 13 comprising unconverted ethylene isrecycled to ethylene oxide production unit 5. Stream 14 comprisingethane is recycled to ethylene production unit 16. Further, a thirdstream may be separated in ethylene/ethane separation unit 12, namely atop bleed stream comprising uncondensable components, such as oxygenand/or argon (said third stream not shown in FIG. 2). Still further,stream 3 may be subjected to hydrotreatment in a hydrotreater unitbefore entering ethylene oxide production unit 5 (said hydrotreater unitnot shown in FIG. 2) to convert any acetylene present.

In the present invention, additional ballast gas, such as nitrogen ormethane, may be added to the ethylene oxide production step. However, itis also envisaged in the above steam cracking embodiments of the presentprocess that the conversion and/or selectivity in the ethyleneproduction step in question (that is to say, the steam cracking step),is tuned depending on the desired amount of ballast gas needed in theethylene oxide production step. That is to say, for example in saidethane steam cracking embodiment, in case the demand for ballast gas inthe ethylene oxide production step is relatively low, conversion in saidethylene production step may be set higher such that relatively lessunconverted ethane is present in the product stream resulting from saidethylene production step. And, conversely, in case the demand forballast gas in the ethylene oxide production step is relatively high,conversion in said ethylene production step may be set lower such thatrelatively more unconverted ethane is present in the product streamresulting from said ethylene production step. Alternatively, conversionin said ethylene production step may be kept constant and additionalballast gas, such as nitrogen or methane, may be added to the ethyleneoxide production step, as mentioned above. For example, the conversionin said ethylene production step may range from 5 to 90%, suitably from10 to 60%.

Alternatively or additionally, the ethane from the stream comprisingethylene oxide, unconverted ethylene and ethane resulting from the stepof producing ethylene oxide is not recycled or not completely recycledto the step of producing ethylene oxide and/or is not recycled or notcompletely recycled to the steam cracking step of producing ethylene,but is used as a fuel for providing heat, by combustion, to the varioussteps of the present process, including one or more of the ethyleneproduction step comprising oxygenate conversion, the ethylene oxideproduction step and the optional ethylene production step comprisinghydrocarbon steam cracking.

The above advantageous embodiment is exemplified in FIG. 2 as describedabove, with the proviso that in the latter embodiment stream 14 is notfed to ethylene production (steam cracker) unit 16, but is used as afuel for providing heat, by combustion, for example to ethyleneproduction unit 2, ethylene production unit 16 and/or ethylene oxideproduction unit 5.

In general, in steam cracking a hydrocarbon stream into ethylene,methane may be produced as a by-product. Separating any methane from thestream comprising ethylene and ethane is not essential in terms ofobtaining the advantages of the present invention as described herein.It is even preferred that methane, if any, is not separated from thelatter stream. In this way, methane may function as a ballast gas, incombination with ethane, in the ethylene oxidation step. This isadvantageous first of all in that the methane does not have beseparated, which is cumbersome, and secondly in that in a case whereadditional ballast gas needs to be added to the ethylene oxideproduction step, this may no longer be needed as the mixture of methaneand ethane may provide a sufficient amount of ballast gas for theethylene oxide production step.

In the above steam cracking embodiments of the present process, thecracking process is performed at elevated temperatures, preferably inthe range of from 650 to 1000° C., more preferably of from 750 to 950°C. The conversion is typically in the range of from 40 to 75 mol %,based on the total number of moles of hydrocarbon provided to thecracking zone. Steam cracking processes are well known to the skilledperson and need no further explanation. Reference is for instance madeto Kniel et al., Ethylene, Keystone to the petrochemical industry,Marcel Dekker, Inc, New York, 1980, in particular chapter 6 and 7.

In the above steam cracking embodiments of the present process, it ispreferred to combine at least part of the stream comprising ethylene andethane obtained from the step of producing ethylene by the conversion ofa stream comprising an oxygenate with at least part of the streamcomprising ethylene and ethane obtained from the steam cracking step,that is to say the step of producing ethylene by converting ahydrocarbon stream (comprising ethane, naphtha, gasoil and/or hydrowax)into a stream comprising ethylene and ethane, prior to sending thestreams to a work-up section. By combining at least part of these twostreams, a more efficient use of the work-up facilities is achieved. Inaddition, by combining at least part of these two streams, also thesmaller fractions in these streams may be more efficiently separated.

Preferably, at least part of the ethylene oxide is converted tomonoethylene glycol (MEG), which is a useful liquid product. Theconversion of ethylene oxide to MEG may be done using any MEG producingprocess that uses ethylene oxide. Typically the ethylene oxide ishydrolysed with water to MEG. Optionally, the ethylene oxide is firstconverted with carbon dioxide to ethylene carbonate, which issubsequently hydrolysed to MEG and carbon dioxide. The water is providedto the MEG zone as a feed containing water, preferably pure water orsteam. The MEG product is obtained from the MEG zone as a MEG-comprisingeffluent. Suitable processes for the production of ethylene oxide andMEG are described for instance in US2008139853, US2009234144,US2004225138, US20044224841 and US2008182999, the disclosures of whichare herein incorporated by reference. The invention is furtherillustrated by the following Example.

Example

In this experiment, ethylene was oxidized into ethylene oxide (EO) overa rhenium-containing catalyst prepared according to US20090281345 andhaving a silver content of 17.5 wt. %, using air as a source of oxygen(oxidizing agent), using ethane as ballast gas, and using ethyl chloride(EC) as moderator.

The experiment was performed in a “single-pass” or “once-through” modewithout any recycle. An inlet gas stream was contacted with the catalystin a U-shaped tubular steel microreactor that was immersed in atemperature-controlled molten metal bath. The inlet gas stream comprised25 vol. % of ethylene, 8.3 vol. % of oxygen, 0.6 vol % of carbondioxide, 260 parts per million by volume (ppmv) of EC, 32.3 vol. % ofethane, the balance comprising nitrogen originating from the air thatwas used as the source of oxygen and from the blend containing EC thatwas used as the moderator.

A gas flow rate of 254 cc/minute was directed through a 4.6 g charge ofcatalyst, providing a gas hourly space velocity (GHSV) of 2,850 hr⁻¹.Total pressure was 16.5 bar gauge. Generation of 3.48 vol. % EO in theproduct stream corresponded to a work rate of 195 kg of product percubic meter of catalyst bed per hour (kg/m³/hr). The catalysttemperature to achieve said target work rate was 244° C.

Results of the experiment are shown in Table 1 below. The experimentshows that ethane can be used as a ballast gas in the oxidation ofethylene to EO. In addition, when using ethane as ballast gas, theselectivity of the ethylene oxidation reaction to EO is high.Furthermore, ethane is converted to only a small extent.

TABLE 1 Oxygen conversion 46.6% Ethylene conversion 15.2% Ethaneconversion 0.7% Selectivity of conversion of ethylene to EO 88.9%

1. A process for the production of monoethylene glycol, comprising thesteps of: a. producing ethylene by converting a stream comprising anoxygenate into a first product stream comprising ethylene and ethanethrough an oxygenate-to-olefins process; b. producing ethylene oxide bysubjecting ethylene and ethane from the first product stream comprisingethylene and ethane to oxidation conditions resulting in a secondproduct stream comprising ethylene oxide, unconverted ethylene andethane; c. recovering ethylene oxide from the second product streamcomprising ethylene oxide, unconverted ethylene and ethane; and d.converting the ethylene oxide to monoethylene glycol through anhydrolysis reaction.
 2. A process according to claim 1, wherein theethylene oxide is first converted with carbon dioxide to ethylenecarbonate which is then hydrolysed to monoethylene glycol and carbondioxide.
 3. A process according to claim 1, wherein a stream comprisingunconverted ethylene and ethane is separated from the second productstream comprising ethylene oxide, unconverted ethylene and ethane and isrecycled to the step of producing ethylene oxide.
 4. A process accordingto claim 1, wherein the first product stream comprising ethylene andethane further comprises methane.
 5. A process according to claim 1,wherein the first product stream comprising ethylene and ethane furthercomprises acetylene and the first product stream comprising ethylene andethane is subjected to hydrotreatment to convert any acetylene prior tosubjecting ethylene and ethane from the first product stream comprisingethylene and ethane to oxidation conditions.
 6. A process according toclaim 4, wherein the first product stream comprising ethylene and ethanefurther comprises hydrogen and at least part of the hydrogen is used toconvert at least part of the acetylene.
 7. A process for the productionof monoethylene glycol, comprising the steps of: a. producing ethyleneby converting a stream comprising an oxygenate into a first productstream comprising ethylene and ethane through an oxygenate-to-olefinsprocess; b. producing ethylene by converting a stream comprising ethaneinto a second product stream comprising ethylene and unconverted ethanethrough a steam cracking process; c. producing ethylene oxide bysubjecting ethylene and ethane from the first product stream comprisingethylene and ethane and the second product stream comprising ethyleneand unconverted ethane to oxidation conditions resulting in a streamcomprising ethylene oxide, unconverted ethylene and ethane; d.recovering ethylene oxide from the stream comprising ethylene oxide,unconverted ethylene and ethane; and e. converting the ethylene oxide tomonoethylene glycol through an hydrolysis reaction.
 8. A processaccording to claim 7, wherein the ethylene oxide is first converted withcarbon dioxide to ethylene carbonate which is then hydrolysed tomonoethylene glycol and carbon dioxide.
 9. A process according to claim7, wherein ethane from the stream comprising ethylene oxide, unconvertedethylene and ethane is recycled to the step of producing ethylene whichlatter step comprises converting a stream comprising ethane into astream comprising ethylene and unconverted ethane.
 10. A processaccording to claim 7, wherein ethane from the stream comprising ethyleneoxide, unconverted ethylene and ethane is recycled to the step ofproducing ethylene oxide and to the step of producing ethylene whichlatter step comprises converting a stream comprising ethane into astream comprising ethylene and unconverted ethane.
 11. A processaccording to claim 7, wherein a stream comprising unconverted ethyleneand ethane is separated from the stream comprising ethylene oxide,unconverted ethylene and ethane, the stream comprising unconvertedethylene and ethane is separated into a stream comprising unconvertedethylene which is recycled to the step of producing ethylene oxide and astream comprising ethane which is recycled to the step of producingethylene which latter step comprises converting a stream comprisingethane into a stream comprising ethylene and unconverted ethane.